Among hydrophobic cluster compounds, non-metal cluster compounds have been administered to a living body on a trial basis for tumor treatment or the like in recent years.
For example, a fullerene, a carbon cluster compound, has been attempted to be used as a photosensitizer in photodynamic therapy, in which a photosensitizer absorbed by tumor cells or by neovascular endothelial cells in tumor tissue is exposed to laser beam irradiation, thereby generating active oxygen to destroy the tumor cells and to eventually eliminate the tumor.
A carborane, a boron cluster compound, has also been attempted to be used as a boron compound in boron neutron capture therapy, in which a boron compound accumulated in tumor cells is exposed to thermal neutron irradiation, thereby emitting α rays to destroy nearby tumor cells.
Metal cluster compounds are conductive or semiconductive and hence in atomized form can be used to realize a wiring method which involves applying such a compound and which can be a substitute for a conventional plating wiring. Therefore application of metal cluster compounds has been investigated in various areas including circuit formation for electronic or information devices and the development of sensors, which investigation has contributed to the development of one aspect of printable electronics technology.
Carbon nanotubes are highly conductive and, since they are carbon compounds, are highly environmentally friendly. With these advantages, carbon nanotubes are expected to be applied to conductive carriers or devices.
For the purpose of administering a non-metal cluster compound that is among hydrophobic cluster compounds to a living body, it is necessary to solubilize the compound. For example, JP 2007-238847 A discloses that a fullerene can be made soluble in water by complexation with a β-1,3-1,6-glucan having a low degree of branching with β-1,6-linked side chains, such a β-1,3-1,6-glucan being exemplified by sizofuran. JP 2006-69812 A discloses that a fullerene can be made soluble in water by complexation with cyclodextrin (α-glucan). JP 2008-222585 A discloses that a carborane can be made soluble in water by complexation with sizofuran. JP 2005-104762 A discloses that a carbon nanotube can be made soluble in water by complexation with sizofuran.
However, these complexes comprising a non-metal cluster compound lack sufficient water solubility for practical use. The complexes also lack sufficient dispersibility in aqueous solutions. These properties make handling of the complexes difficult.
Regarding a metal cluster compound that is among hydrophobic cluster compounds, particles of a metal cluster compound existing not independently but forming a regular structure exhibit novel electronic, optical, magnetic properties that cannot be observed when the particles independently exist. Various studies for applying such novel properties to advanced electronics, optical devices, and the like have been actively conducted in recent years. However, since there are no specific interactions between metal cluster compound particles, the particles hardly aggregate in a self-organized manner. In contrast, a high-molecular chain has a particular higher-order structure formed in a self-organized manner and is capable of serving for aggregation or dispersion of independently existing metal cluster compound particles. For example, JP 2006-205302 A discloses that gold can be made soluble and dispersible in water by complexation with sizofuran. However, such a complex containing a metal cluster compound lacks sufficient water dispersibility and water solubility for practical use.